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Unformatted text preview: Molecular Dynamics simulations Lecture 10: Ionic Interactions Dr. Olli Pakarinen University of Helsinki Fall 2011 Original lecture notes by Dr. Jani Kotakoski, 2010 Ionic Compounds I Ionic compounds are materials which are held together via electrostatic interactions between oppositely charged bodies I Electrons are localized around the atoms, as compared to free electrons in a metallic system I Correspondingly, ionic compounds are insulators as solids I However, in liquid state they conduct electricity (the ions are free to move about) I Ionic materials often have high melting and boiling points I They are also very hard and brittle I The typical example of an ionic solid is sodium chloride (NaCl), i.e., table salt I It is a typical alkali halide ( X- Y + ), with a simple rock salt structure I Ionic liquids have melting point below room temperature I Some are glass formers, i.e. do not form crystalline solids I In reality, all ionic compounds exhibit at least a tiny bit covalent nature I However, e.g., in hexagonal boron nitride structure the covalency is (almost) impossible to be seen from DFT calculations I Also, covalently bonded materials often exhibit some charge...
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